Multi-cathode tube counter circuits



June 16, 1959 R. TOWNSEND 2,890,827

- MULTI-CATHODETUBE COUNTER CIRCUITS Filed March 5, 195a s Shets-Sheet 1 INVENTOR R01 Tbil/VJEND BY H MW ATTQRNEY June 16, 1959 R. TOWNSEND 2,890,827

MULT I-CATHODE TUBE COUNTER CIRCUITS Filed March 5, 1956 3 Sheets-Sheet 2 CARRY O U T 27C 0 Lt ATTORNEY;

June 16, 1959 R. TOWNSEND 2,890,827

MULTI-CATHODE TUBE COUNTER CIRCUITS Filed March 5, 1956 I 3 Sheets-Sheet 3 oooooooo 42 M44 3: FIG. 3. 2? I INVENTOR R/u r/r Tum save r ATTORNEYS United States Fatent MULTI-CATHODE TUBE COUNTER CIRCUITS 'Ralph Townsend, Manchester, Mass, assignor to The British Tahulating Machine Company Limited, London, England, a British company Application March 5, 1956, Serial No. 569,321

Claims priority, application Great Britain March 9, 1955 15 Claims. (Cl. 235-611) This invention relates to circuits for use with multicathode gas-filled counting tubes which may be connected to form a multi-denominational accumulator.

When several multi-cathode counting tubes are connected in cascade to form a counter, the requirements for the carry circuits between adjacent denominations are not stringent. There is no interaction with the input pulses, which are fed to the lowest denomination only. Various forms of carry circuit are described in an article entitled The Use of Cold Cathode Counting Tubes in Cascade, by D. T. Whelan, in Electronic Engineering, March 1954, pp. 118-9.

In an accumulator, input pulses may be applied to all the denominations simultaneously, so that the carry circuits must be arranged in such a way that a carry pulse cannot interfere with the operation of a counting tube by the input pulses.

It is an object of the invention to provide a carry circuit for use with a multi-cathode gas-filled counting tube.

It is a further object of the invention to utilise the same valve for effecting carry transfer from a first to a second counting tube, and for reading out the value registered by the first counting tube.

It is another object of the invention to employ this carry valve for reading out either the value registered by the counting tube, or the complement of that value.

According to the invention valueregistering apparatus, employing a multi-cathode discharge counting tube, has cyclically operable means for entering values by stepping the discharge successively on to the individual cathodes, a load circuit for one of the cathodes, a bi-stable device, means, operated by the flow of discharge current through the load circuit, for triggering the bi-stable device from a first to a second stable state, and a switching device operable at a predetermined point in the entry cycle to apply a voltage output from the bi-stable device to a further counting device, which is operable by the voltage output provided by the bi-stable device in the second state. Each cathode may have a first load circuit, switching means for blocking current flow through the load circuit, a second load circuit providing an alternative current path if the first is blocked, a bi-stable device which is triggered by current flow through the second load circuit, and a cyclically operable utilisation device operated by the triggering of the bi-stable device, the switching means being synchronised with the utilisation device. A single bi-stable device may be triggered either under control of any one of the cathodes, or under control only of a predetermined cathode.

The invention will now be described, by way of example, with reference to the accompanying drawings showing the invention embodied in a punched card controlled machine in which multicathode counting tubes of the type manufactured and sold under the trade name Dekatron are employed as stages of an accumulator. Inthc drawings, 7 v I ice Figure 1 shows the card sensing and control circuits in schematic form;

Figure 2 shows the counting tube circuit of a stage of the accumulator other than the highest denomination stage;

Figure 3 shows the counting tube circuit of the highest denomination stage.

Referring now to Figure 1, information as to whether an entry into the accumulator is to be additive or subtractive is sensed from a card by a conventional brush sensing mechanism 1. The feeding of the card closes card lever contacts 2, and the sensing of a designation hole in a particular column, indicating that a subtractive entry is required, completes a circuit for a winding 3P of a designation relay from the zero potential line on the right of the drawing through machine contacts C0, closed when the machine starts to operate, through contacts 2, mechanism 1, winding 3P to the positive supply line on the left of the drawing. The designation relay operates to close contacts 3A and thus complete an energising circuit for its own hold winding 3H over cam contacts C1. This relay is thus held up until contacts C1 are opened near the end of a machine cycle. The closing of contacts 3A also completes a circuit for energising an add/ subtract relay 4 over cam contacts C2. Relay 4 in operating closes contacts 4A to complete a self hold circuit over cam contacts C2 and cam actuated contacts C3. The latter contacts are opened just before zero index point time in each sensing cycle but relay 4 can still hold over contacts 3A and C1. Relay 4 also actuates changeover contacts 4B the effect of which is de scribed later.

When an additive entry into the accumulator is re-' quired the add/ subtract relay 4 is not energised so that the contacts 413 remain in the position shown.

The card sensed by the mechanism 1 is then fed to a second sensing station 5, and in so doing closes card lever contacts 6 to render the mechanism 5 operative. At this second station the number to be entered into the accumulator is sensed by a series of brushes each corresponding to one denomination. Each brush controls a brush relay and for simplicity of illustration only one of the brush relays is shown in Figure l. A winding 6P of this brush relay is energised when its associated brush 5a senses a hole indicating a value in the denomination to which the brush relates, the 9 index point being sensed first. A circuit is then completed from the zero potential line over cam contacts C4, contacts 6, mechanism Sand winding 6P to the positive supply line.

The energisation of winding 6P actuates changeover contacts 613 and closes contacts 6A to complete a circuit for the hold winding 6H of the brush relay over contacts C3, so that the brush relay is held operated and its changeover contacts 6B held actuated until the contacts C3 are opened just before the zero index point p is sensed.

guish it again at each index point so that thyratron 7 produces an output pulse at each index point.

When the brush relay is energised by the sensing of a hole at a particular index point, the output pulses from the thyratron are fed to a pulse line PL through the contact set 4B and the shifted contact set 6B. The brush a relay is held energised until just before zero, so that the number of pulses appearing on the line PL is equal to the value of the sensed digit. These pulses are fed to a counting tube to enter the corresponding value. It will be appreciated that with the contact set 413 actuated to cause a, subtractive entry into the accumulator, the pulses appear on line. PL until the moving contact of set 6B is displaced by operation of the brush relay and are then suppressed.

Thus, if for example, a five is sensed by the brush, the five pulses corresponding to index points 5, 4, 3, 2 and 1 appear on line PL for additive entry whereas for subtractive entry the four pulses corresponding to index points 9, 8, 7 and 6 appear on the line PL.

The pulse line PL feeds the pulses to the input circuit of the counting tube 12 shown in Figure 2, where they are applied to the guide electrodes of the tube. The line PL is connected to one side of a capacitor 13 the other side of which is connected to the cathode of a diode 14. The pulses on the line PL are fed through capacitor 13 and diode 1-4 to the junctionof two resistors 15 and 16. The resistor 16 is connected to the second guide electrode and forms a pulse integrating circuit with a capacitor 17 connected between the second guide electrode and ground. The other end of the resistor 15 is connected to the first guide electrode. Thus, a pulse on the line PL is applied to both guide electrodes. A single pulse on the line FL is effective to cause transfer of the discharge from one cathode to the next, via the guide electrodes. eration of this form of multi-cathode tube is described in detail in an article entitled The Dekatron, by. R. C. Bacon and J. R. Pollard, published in Electronic Engi-. neering, May 1950. The DC. potential of the guide electrodes is established by means of a potentiometer formed by resistors 60 and 61 connected between the positive supply line and ground. The junction of these two resistors is connected via a resistor 62 to the first guide electrode. There is a connection from the second guide electrode to this junction through resistors 16, 15 and 62'.

Such stepping may cause the discharge to be located on, or to pass the zero cathode of the tube, in which event a carry pulse must be generated to increase by one the value registered by the counting tube of the next higher denominational order. To provide for this each cathode of the counting tube 12 is connected through a first diode such as 18 and resistor such as 19 to a zero potential line 20, the diode being poled to permit current flow to such line. Each cathode is also connected through a further, similarly poled diode 21 to a common carry line 22 whichin turn is connected to line through a resistor 23.

Normally the current from any cathode on which the discharge is located, flows through the comparatively low impedance path constituted by its associated diode 18 and resistor 19 to line 20 so that the voltage change of the carry line 22 is small. This carry line is connected through capacitor 24 and resistor 25 to the control grid of a gas-filled triode carry valve 26. The junction of the diode 18 and resistor 19 associated with the zero cathode is connected to a source of positive potential over normally closed contacts 27A of a read-out relay 27 (Figure 1). Thus when the discharge is located on the zero cathode the cathode current is prevented from flowing through the diode 18 and is forced to flow through the associated diode 21, the common carry line 22, and the resistor 23 to earth. This current path being of relatively high impedance the voltage change on the carry line is suiiicient to fire the carry valve 26 which thus serves to indicate when the value registered by the tube 12 arrives at or passes through the ero position.

The carry valve may be fired at any time during the entry of a value into the tube 12 depending upon such. value and the value already registered by the tube. The transfer of a carry to the tube of the next higher denomi- The opnation is, however, delayed until completion of the value entry cycle.

Such transfer is eifected over the line marked Carry Out which is connected to a line, in the input circuit of the tube of the next higher denomination, corresponding to the line marked Carry-In in the circuit of tube 12. This latter line terminates atone of the fixed contacts of a changeover contact set 30A controlled by a carry relay 30. (Figure 1). Relay 30 is energised by cam actuated. contacts C7 at Zero index point time and remains energised a sufficient time to permit a long carry to clear through the acctunulator as explained later.

The moving contact 30b of set 30A normally engages the other fixed contact and is thus connected through resistor 31 to the HT supply line. The moving contact is connected to an integrating circuit 34, 35 serving to remove spurious signals due to the operation of the contacts, and to one side of capacitor 32. The other side of capacitor 32 is connected through resistor 36 to line 20 and also through diode 33 to the point where diode 14 is connected to the input circuits to the guide electrodes of tube 12.

Thus upon operation of the carry relay 30 (Figure l) the potential applied to. capacitor 32 isswitched from a relatively high value to the relatively low value at the anode of the valve 26 in the next lower denomination stage, and a pulse is applied through capacitor 32 and diode 33, to the guide electrodes to step the discharge of tube 12 on one step, if the valve 26 has been fired.

As previously mentioned, the carry relay 30 is maintained energised long enough for a long carry to clear through the accumulator. Thus where several successive stages of the accumulator are registering the value 9, the transfer of a carry to the first of these stages steps the discharge in the stage counting tube on to its zero cathode and thus generates a carry pulse for the next stage, where the operations are repeated and the carry propogated through the succession of stages. At the end of the card sensing cycle the HT supply to the carry valves is interrupted by cam actuated contacts C8, thus restoring all the carry valves to their non-conducting state.

The diodes 14 and 33 isolate the entry and carry input circuits from each other and the diodes 37 and 38 serve respectively to restore the capacitor 13 and to prevent positive pulses from entering the tube driving circuit.

The carry valve 26 of each stage also serves to provide an indication of the value registered in the tube 12 during read-out by causing it to fire at a time instant corresponding to the value of the cathode on which the discharge is located. This is effected by scanning the cathodes of the tube 12 with a commutator in the following manner.

The read-out relay 27 (Figure 1) is energised upon closure of cam controlled contacts C9, at the end of a card group for example, and operates to open the contacts 27A over which the positive bias was applied to the diode 18v in the zero cathode circuit, and to close contacts 273 and 27C which connect the anode of the carry valve 26 to the HT supply line through a connection (not shown) between sockets 40, a punch magnet 41 and cam controlled contacts 42. The contacts 27C also connect the HT supply line through cam controlled contacts 43 to a commutator 44. Contacts 27D disconnect the normal HT supply to valve 26.

The junctions of the diodes 18 and the resistors 19 of all the cathodes of tube 12 are individually connected to the moving contacts of ten changeover contact sets 45A, the two fixed contacts of each of which are connected to commutator segments corresponding to the true and co nplementary versions respectively of the value assigned to the tube cathode connected to the moving contact in each case. The changeover sets 45A are controlled by a true/complement relay 45' (Figure 3) in dependence upon whether the value registered in the accumulator is in true or complementary form. The control of relay 45 is described later in the reference to Figure 3.

The two cam controlled contacts 42 and 43 are operated at each index point as the value registered into the accumulator is punched into a card. Thus with contacts 27C closed a potential is applied by the successive operations of contacts 43, to each of the commutator segments in turn and over the changeover contacts 45A to the cathode of each of the diodes 18 in turn. When the diode 18 of the counting tube cathode on which the discharge is located is thus biased by the potential from the commutator, the current from such cathode is caused to flow through the corresponding diode 21 to the common carry line 22.

Contacts 27C also apply potential over contacts 42, magnet 41 and contacts 27B to the anode of carry valve 26 each time contacts 42 are closed so that on scanning or the cathode on which the counting tube discharge is located, the valve 26 fires and so energizes the punch magnet 41. Since the card on which the read out is to be punched is fed in synchronism with the scanning of the cathodes the punching takes place at an index point corresponding to the value assigned to the cathode on which the discharge is located.

In the event of a complementary value being registered in the accumulator i.e. as the result of a subtraction the actuation of the changeover contacts 45A would cause the, cathodes to be scanned in reverse order so that punching would take place at an index point corresponding to the complement of the value assigned to the cathode on which the discharge rests.

Referring now to Figure 3, there is shown the highest denomination stage of the accumulator which difiers from preceding stages, such as that shown in Figure 2, only in that it is provided with a complement sensing circuit and that the Carry Out hne is connected to the Carry In line of the lowest denomination stage to effect an end around carry during subtraction. The details of the tube circuit are not therefore shown in full it being assumed that these are the same as shown in Figure 2, and the same references are used in both figures for corresponding items.

The operation of the complement sensing circuit is as follows. At the end of a card group and immediately prior to read-out the cam actuated contact C is closed to apply a bias potential to the cathode of the diode 18 ofthe 9 cathode of the counting tube.

v This cathode is connected over line 51, capacitor 52 and resistor 53 to the grid of a valve 54 similar to the carry valve 26. If the value registered in the accumulator is in complementary form, the discharge in the counting tube of the highest denomination stage will be located on the 9 cathode so that the application of the bias will cause an impulse to be applied to the grid of valve 54, to fire it. The carry valve 26 will not be fired at this time because its anode supply circuit is interrupted at contacts C8.

The anode circuit of valve 54 includes a cam actuated contact C11 and true/ complement relays such as 45 each of which is energised when the valve 54 fires, and each operates the changeover contacts 45A in one of the stages of the accumulator so that a complementary read-out takes place. The contacts C8 restore the anode potential to the carry valve 26 in the highest denomination circuit, when the complement sensing has been effected, in readiness for the scanning of the cathodes by the commutator in the manner previously described. The contacts C11 interrupt the anode supply to valve 54 after read-out so that it is extinguished in readiness for further complement sensing.

The accumulator described above may be used in conjunction with a machine, generally known as a reproducer, similar to that described in British patent specification No. 442,534. These are a reading card feed and a punching card feed. The reading feed has two sensing mechanisms corresponding to the mechanisms 1 and 5.

'1-The punching card feed has a set of punch magnets each corresponding to the magnet 41, which may be operated in a timed manner to punch a hole at a required index point in a column of a card.

Such a machine has a set of cams, for controlling the timed operation of contacts, associated with each feed. The cam contacts, such as C0, C1, C2 etc., which are effective during entry and carry operations may be operated by cams mounted on the reading feed cam shaft. The cam contacts, such as C8, which are effective during read out may be operated by cams mounted on the punching feed cam shaft.

It will be appreciated that the magnet 41 may be used to control the setting of a printing member, instead of controlling punching. Printing mechanisms operable by timed impulses for character selection are well known.

Although the invention has been described as applied to a decimal accumulator, it may equally well be applied to accumulators Working in other scales, such as duodecimal, and to accumulators for mixed scales, such as British or Indian currency.

What we claim is: p

1:. Value registering apparatus employing a multicathode discharge counting tube, having means for entering values by stepping the discharge successively on to the individual cathodes, a first load circuit for each cathode, which normally provides a path for discharge current flowing to that cathode, cyclically operable switching means for blocking current flow through the load circuit of each cathode in turn, a second load circuit providing an alternative current path for each cathode when current flow through the first load circuit is blocked, a bi-stable device, means, operated by the flow of current through the second load circuit, for triggering the bi-stable device from a first to a second state, and a cyclically operable utilisation device operable by the triggering of the bi-stable device, the switching means being synchronised with the utilisation device.

2. Value registering apparatus employing a multicathode discharge counting tube, having means for entering values by stepping the discharge successively on to the individual cathodes, a first load circuit for each cathode for carrying discharge current flowing to that cathode, a first switching device for blocking current flow through the load circuit of each cathode in turn, a. second switching device for blocking current flow through the load circuit of a predetermined cathode only, a second load circuit providing an alternative current path for each cathode when current flow through the first load circuit is blocked, a bi-stable device, means, operated by the flow of current through the second load circuit, for triggering the bi-stable device, and means for rendering either the first or the second switching means efiective.

3. In value registering apparatus having a multicathode gas discharge tube and means for registering a value by establishing the discharge on a given one of said cathodes; read out means comprising a first and a second circuit for each said cathode operatively connected to pass cathode current when the discharge is located on that cathode, switching means operating on the first circuits of said cathodes in sequence in a scanning cycle for causing discharge current flowing through a first circuit to be diverted to the second circuit, a bistable device, and means responsive to diversion of current to a second circuit for triggering said device from a first to a second state to indicate the registered value by the time in said cycle at which said bistable device is triggered.

4. In value registering apparatus having a multicathode gas discharge tube and means for establishing the discharge on a given one of said cathodes to represent a value to be registered; read out means comprising, for each cathode, a first circuit and a second circuit both operatively connected to the cathode to pass cathode current when the discharge is located on that cathode, switching means, operating in sequence in a scanning cycle onthe.

first circuits of said cathodes, for preventing passage of discharge current through each of said first circuits in turn, whereby current flowing through the first circuit of the cathode on which the discharge is located is diverted to the second circuit when the switching circuit operates on that first circuit, a bi-stable device, and means responsive to the flow of current in a second circuit for triggering said bi-stable device from a first to a second state to indicate the registered value by the time in said cycle at which said bi-stable device is triggered.

5. Read out means as claimed in claim 4 in which each said first circuit comprises a unilaterally conducting device and a resistor in series, and said switching means comprises means for applying to the junction of said unilaterally conducting device and said resistor of each cathode in turn a voltage preventing the flow of discharge current through said unilaterally conducting device.

6. In value registering apparatus having a multi-cathode gas discharge tube and means for establishing the discharge on a given one of said cathodes to represent a value to be registered; read out means comprising, for each cathode, a first circuit and a second circuit both operatively connected to the cathode to pass cathode current when the discharge is located on that cathode, each said first circuit comprising a unilaterally conducting device and a resistor in series and said each said second circuit includes an impedance common to all said second circuits and of substantially larger value than the individual values of said resistors, switching means for applying a voltage to the junction of said unilaterally conducting device and said resistor of each of said first circuits in sequence in a scanning cycle, said voltage preventing flow of discharge current through said unilaterally conducting device, whereby current flowing through the first circuit of the cathode on which the discharge is located is diverted to the second circuit when the switching circuit operates on that first circuit, a bi-stable device, and means responsive to the flow of current in a second circuit for triggering said bi-stable device from a first to a second state to indicate the registered value by the time in said cycle at which said bi-stable device is triggered.

7. Read out means as claimed in claim 6 in which said bi-stable device isa gas discharge tube having a control grid and said current responsive means cornprise means for applying to said control grid the voltage across said common impedance.

8. In value registering apparatus having a multi-catlrode gas discharge tube and means for establishing the discharge on a given one of the cathodes to represent a value to be registered, read out means comprising a commutator, a first circuit and a second circuit for each said cathode, each said first circuit comprising a unilaterally conducting device and a resistor connected in series to the associated cathode, two-position switch means connecting said commutator to the junctions between said unilaterally cond ucting devices. and. said resistors in a first order and in a second order according as said switch means are in a first position and a second position respectively, said commutator applying in a scanning cycle to each of said junctions in succession a voltage preventing the passage of cathode discharge current through each unilateral-1y conducting device in succession, a second circuit connected to each of said cathodes, a common impedance forming part of each said second circuit, and a bistable device responsive to the current in said common impedance which has a value substantially greater than the value of any said resistances, the greater part of the discharge current normally flowing through the first circuit of the cathode on which the discharge is situated until the commutator applies said voltage to the said junction of that cathode, when the discharge" eurrentflowing through the first circuit is diverted to the second circuit, and the bi-stable device is operated. I

9. In multi-denominational value registering apparatus having a multi cathode gas discharge tube for each denomination and means for establishing the discharge in each said tube on a given one of the cathodes to represent the value to be registered in the respective denomination; read-out means comprising a common commutator, a first circuit and a second circuit for each said cathode of each said tube, each said first circuit comprising a unilaterally conducting device and a resistor connected in series to the associated cathode, an impedance for each said tube having a value substantially greater than the value of any of said resistors, the second circuits of the cathodes of each tube all including the impedance for the tube, the major part of the discharge current therefore normally passing through the first circuit of the cathode on which the discharge is located, means including said commutator for applying successively to each of said unilaterally conducting devices of each tube, a Voltage preventing the passage of cathode discharge current therethrough so that the cathode discharge current is diverted to said second circuits, said voltage being applied to said devices of the corresponding cathodes of all said tubes simultaneously and a bi-stable device for each said tube responsive to the current in the impedance of the tube and operated when said voltage is applied to the device of the cathode on which the discharge is located.

10. A multi-denominational accumulator comprising a multi-cathode gas discharge tube for each denomination, means for applying to each said tube a succession of discharge shifting pulses corresponding to the value to be entered in the denomination, a bi-stable device for each said denomination, switch means operatively connected to the zero-representing cathode of each said tube for causing said bi-stable device to be triggered when the discharge is located onthe zero-representing cathode of the respective tube, carry means for each said tube except the tube of lowest significance controlled by the bi-stable device of the tube of next lower denominational significance for applying a pulse into the respective tube, read out means for reading out the value registered in said tubes, said read-out means comprising a common commutator, a first circuit and a second circuit for each said cathode of each said tube, each said first circuit comprising a unilaterally conducting device and a resistor connected in series to the associated cathode, an impedance for each. said tube having a value substantially greater than the value of any of said resistors, the second circuits of the cathodes of each tube all including the impedance forthe tube, the major part of the discharge current therefore normally passing through the first circuit of the cathode on which the discharge is located, means includingsaid commutator for applying successively to each of said unilaterally conducting devices of each tube a voltage preventingthe passage of cathode discharge current therethrough so that the cathode discharge current is di-' verted to said second circuits, said voltage being applied to said devices of the corresponding cathodes of all said tubes simultaneously, and means for rendering said bistable devices responsive to the current in the impedances of the respective tubes, the bi-stable devices of any tube being operated when said voltage is applied to the cathode on which the discharge is located.

11. A multi-denominational accumulator as claimed in claim 10 comprising also record card sensing. means controlling said pulse ap'plyin'g means to shift in a cycle the discharge in each tube a number of cathodes equal to the value on therecord card.

12. A multi-denominational accumulator as claimed in claim 11 comprising also an electromagnetic relay for each said tube having contacts operatively connected to said bi-stable device and controlling the pulse applying: means of the tube of next higher significance for carry entry and means for energising said electromagneticirelay at a predetermined point in said cycle.

13. A multi-denominational accumulator as claimed in claim 10 comprising also a record card punching mechanism including a punch operating magnet for each said tube, each said magnet being operatively connected to the bi-stable device of the respective tube so as to be operated when said device is triggered, and means for operating said punching mechanism under control of said commutator.

14. A multi-denominational accumulator as claimed in claim 10 comprising also two-position switch means for each said tube connecting the junction of the unilaterally conducting device and the resistor of said first circuit of that tube to said commutator in one order and in reverse order according as the two-position switch means are in one position and the other position respectively, to read out the value registered in the tube in true form and in complement form respectively, a second bi-stable device, means for controlling said second bi-stable device by the discharge current to the nine representing cathodes of the multi'cathode tube of greatest denominational significance, and means operated by said second bi-stable device for operating said two-position switch means to said other positions.

15. Value registering apparatus comprising a first and a second multi-cathode discharge counting tube, means for applying to the tubes value-representing pulses causing the discharge in each said tube to step successively on to the individual cathodes, said pulses being applied to said tubes concurrently according to an entry cycle, a load circuit for one of the cathodes of said first tube, a bi-stable device having a first and a second stable state and giving a voltage output when in said second stable state, means operated by the flow of discharge current through said load circuit for triggering said bi-stable device from said first stable state to said second stable state, and a switching device operable at a predetermined point in the entry cycle and, when operated, applying said voltage output to operate said second tube, said bi-stable device being operatively inefiective on said second tube except when said switching device is operated.

References Cited in the file of this patent UNITED STATES PATENTS 2,473,159 Lyman June 14, 1949 2,568,177 Vroom Sept. 18, 1951 2,774,534 Dunn Dec. 18, 1956 2,807,419 Rabenda Sept. 24, 1957 

